Stripline having two ground planes mechanically spaced by removable longitudinal electrical connectors disposed parallel to signal conductor



June 7, 1966 BUTLER 3,255,426

STRIPLINE HAVING TWO GROUND PLANES MEGHANICALLY SPACED BY REMOVABLE LONGITUDINAL ELECTRICAL CONNECTORS DISPOSED PARALLEL TO SIGNAL CONDUCTOR Filed March 9, 1964 United States Patent STRIPLINE HAVING IWO GROUND PLANES ME- CHANICALLY SPACED BY REMOVABLE LONGI- TUDINAL ELECTRICAL CONNECTORS DIS- POSED PARALLEL TO SIGNAL CONDUCTOR Jesse L. Butler, Groton Road, RED. 2, Nashua, N .H.

Filed Mar. 9, 1964, Ser. No. 350,467 16 Claims. (Cl. 33384) mission of the parallel plate and other undesired transmission line modes. A particular difiiculty arises in high frequency circuitry due to the necessity for close lateral spacing of the ground plane connections bridging the inner conductor for adequate mode suppression purposes. Heretofo-re such ground plane interconnections have been made by using a multiplicity of conventional fastening devices such as screws or rivets, each of which is spaced less than one-half wavelength (through the dielectric) from the immediately adjacent fastening device. A configuration that is electrically similar utilizes the technique of completely encasing the dielectric and the inner conductor in a conductor structure of tubular wave guide form.

Both of these techniques have severe limitations in particular applications. For example, at high operating frequencies more fasteners are needed for mode suppressing purposes than are required merely for mechanically fastening the stripline assembly together. In addition, after the'circuit has been assembled in this manner, it is difficult and expensive to disassemble it to make adjustments. Similar limitations are encountered where an encasing conductor is used, whether in the form of conductive foil wrapped over the edges of the ground planes of the circuit and soldered in place or a unitary mode suppressing-ground plane configuration. In either case it is frequently impossible to disassemble the resulting package for modification or test without destroying it. A further limitation of such techniques is encountered where soldering must be used because of the temperature limitation of the dielectric materials employed in the circuitry.

It is an object of this invention to provide a novel and improved microwave circuit of the strip transmission line type which is more economical to manufacture, particularly in complex configurations.

Another object is to provide a novel and improved microwave circuit assembly which can be tested and then easily disassembled for modification or repair, for example.

In-accordance with the invention there is provided a high-frequency electric circuit comprising an inner conductor, dielectric material disposed on each side of the inner conductor and a pair of parallel planar outer conductors or ground planes which are spaced from the inner conductor by the dielectrics. The dielectrics are of greater width than the inner conductor but, where solid dielectrics are employed, that width should be less than one-half the wavelength (A) in the dielectric material at the highest operating frequency of the circuit. Disposed on each side of the pair of dielectrics is an elongated deformable mode suppressing electrical conductor which has a plurality of spaced contact points along its length. Each mode suppressing conductor is f-rictionally secured between the outer conductors and in electrical contact therewith so that the mode suppressing conductors complete electrical circuits between the outer conductors along paths generally parallel to the inner conductor. The outer conductors are secured together (securing also the mode suppressing conductors and typically the inner conductor and dielectrics) with conventional fastening means at spaced points independent of the frequency at which the circuitry is to be used (as they perform only a mechanic-a1 function). The two mode suppressing conductors, extending parallel to the inner conductor, preferably are compressed and distorted somewhat so that they are securely fastened in position in frictional engagement with the outer conductors. This structure may be assembled, tested, and disassembled, if necessary, with relative ease.

The microwave assembly is adapted for use both with transmission lines and with more complex microwave circuitry configurations, such as multiport devices, and is of particular advantage in connection with the design of complex microwave circuitry.

Other objects, features and advantages of the invention will be seen as the following description of preferred embodiments thereof progresses, in conjunction with the drawing, in which:

FIG.-1 is a diagrammatic view of a microwave circuit;

FIG. 2 is a top view of apparatus constructed in accordance with the invention forming the circuit shown in FIG. 1;

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 2;

FIG. 4 is a second embodiment of the invention in the same microwave circuit form as shown in FIG. 2;

FIG. 5 is a sectional view taken along the line 5--5 of FIG. 4; and

FIGS. 610 illustrate other types of mode suppressing conductors for use in the practice of the invention.

The circuitry shown in FIG. 1 is a multiport device having an inner conductor configuration following the paths indicated and including a ring 10 and four connecting lines 12, 14, 16, and 18. A first form of circuit constructed in accordance with the invention is shown in FIG. 2 and a second form of the same circuit is shown in FIG. 4.

In FIGS. 2 and 3 each line includes a center conductor 20 shown in FIG. 3. This is a thin elongated planar type of conductor which may be of the etched circuit type. Disposed on each side thereof is a sheet of dielectric material 22, 24, each of which is wider than the center conductor 20 and extends transversely beyond the width of the center conductor as shown in FIG. 3. On the outer surface of each dielectric 22, 24 are two parallel outer conductors 26, 28 which in turn extend beyond the limits of the dielectrics 22, 24. These conductors are electrically connected together by means of mode suppressing conductors in the form of helixes 30, 32, one disposed on each side of the dielectrics, in spacing such as to suppress the parallel plate mode and other undesired transmission line modes, e.g., TE The helixes 30, 32

extend along, generally parallel to but spaced from, theinner conductors 20 of the configuration shown in FIG. 1. As shown in FIG. 2, the two ground planes 26, 28 are secured together with mechanical fastenings' 34, such as screws or bolts and nuts, in conventional manner such that the side mode suppressing members are frictionally secured therebet-ween.

It will be seen that this assembly may be readily disassembled for modification of the configuration of the circuitry, the dielectric sheets 22, 24, or the location of the mode suppressing conductors 30, 32 themselves. In addition, it is relatively easy to locate the mode suppressing conductors, and where they are supplied in long lengths, they may be cut to the desired length and disposed in the position against the dielectric sheets 22, 24.

Rather than completely eliminating the dielectric 22, 24 beyond a predetermined point outside the edges of the center conductor 20, the dielectric sheets may have slots 36 formed therein, as shown in FIG. 4, in which the mode suppressing conductors 30, 32 are disposed in the slots in the similar locations. Relatively narrow ground plane bridge conductors 26', 28', connected to foil 38 laminated to the dielectric 22', 24', are employed and, again, as indicated in FIG. 5, the mode suppressing conductors 30', 32 are compressed and deformed so that excellent electrical engagement with the ground plane structures is provided. In the arrangement shown in FIGS. 4 and 5, the ground plane structures are formed by the foil 38 laminated to the outer surfaces of the dielectric sheets and bridging members 26', 28' which are secured together with conventional fasteners such as bolts 40 and nuts 42. A roughened edge surface at 44 on these rigid outer conductor bridges 26', 28' may be provided to insure good electrical connection to the foil outer conductors 38 or RF' gasket type of woven or braided type mesh may be compressed between the foil 38 and the rigid conductors 26', 28' to complete the electrical circuit. In some cases it may be desirable to solder the plates to the foil to seal out moisture, for example.

The mode suppressing conductors may take a variety of forms, but in general they should be flexible and preferably of indeterminate length. The contact points, if separated, should be spaced from one another a distance not greater than one-half wave length. In addition to the helix form of flexible, elongated mode suppressing conductor, other suitable forms are shown in FIGS. 6-10. The element conductor in FIG. 6 is a tube 41 with roughened or corrugated surface or with fluted elements 43 extending around its periphery, either as rings or as a continuous or interrupted helix for example. Another arrangement is shown in FIG. 7 in which is provided a web 45 having a plurality of individual spring elements 46, defining opposed fingers 48, 50 secured to it. This flexible member has flexible deformable surface elements as do the other mode suppressing conductors. Another mode suppressing conductor is shown in FIG. 8 in the form of a serpentine strip 52 having contact points in the form of sharp angles 54 that extend perpendicular to the major length of the strip. The dimensions of the angles may be modified as indicated in FIG. 9. Still another configuration is an arrangement of contact elements 56 in offset or staggered relation on a strip 58, as shown in FIG. 10, which provides a resilient element with the plurality of sharp contact surfaces for making electrical contact with the ground planes 26, 28. Other mode suppressing conductor configurations, similar to the above and including others having a continuum of contact points, for example, will be apparent to those skilled in the art.

It will thus be seen that the invention provides a microwave circuit assembly incorporating novel mode suppressing conductors in an arrangement which is easy to assemble and disassemble and which provides the desired electrical mode suppression characteristics. While preferred embodiments of the invention have been shown and described, further modifications thereof will be apparent to those skilled in the art, and therefore, it is not intended that the invention be limited thereto or to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.

What is claimed is:

1. A microwave circuit component comprising a pair of outer conductors of indeterminate length positioned in superposed spaced relation,

a conductor of corresponding length positioned between said outer conductors and extending in a direction parallel to said outer conductors,

said inner conductor being narrower than said outer conductors,

dielectric material disposed between said inner conductor and each said outer conductor so that said inner conductor is in insulated, spaced relation with respect to said outer conductors,

an elongated mode suppressing electrical conductor,

and

means for releasably securing said mode suppressing conductor between said outer conductors in electrical contact therewith and in spaced relation and substantially parallel to said inner conductor.

2. The component according to claim 1 wherein said mode suppressing conductor has a plurality of electrical contact points spaced along its length, said contact points being spaced apart a distance less than a half wavelength at the highest operating frequency of the circuit.

3. The component according to claim 2 wherein said mode suppressing conductor includes a helix of wire.

4. The component according to claim 2 wherein said mode suppressing conductor includes a flexible member with a plurality of contact members disposed thereon and extending in opposite directions therefrom.

5. A composite high-frequency electrical circuit comprising a pair of parallel, planar, outer conductors,

a planar inner conductor in parallel with and positioned between said outer conductors,

said inner conductor being of less width than said outer conductors,

dielectric material disposed between said inner conductor and each outer conductor so that said inner conductor is positioned in insulated, spaced relation with respect to said outer conductors, and

two elongated, deformable mode suppressing electrical conductors, said mode suppressing conductors being frictionally secured between said outer conductors on either side of said inner conductor substantially parallel to and spaced therefrom by said dielectric material so that the effective separation between said mode suppressing conductors is less than one-half wavelength in said dielectric material at the highest operating frequency of the circuit.

6. A microwave circuit comprising a pair of planar outer conductors of indeterminate length positioned in superposed spaced relation,

a planar inner conductor of corresponding length disposed between said outer conductors and extending parallel thereto,

said inner conductor being narrower than said outer conductors,

solid dielectric material of a width greater than that of said inner conductor disposed between said inner conductor and each said outer conductor for supporting said inner conductor in insulated spaced relation to said outer conductors,

two elongated, deformable, mode suppressing electrical conductors, said mode suppressing conductors being positioned in electrical contact with both said outer conductors on opposite sides of said inner conductor substantially parallel and spaced from said inner conductor by said solid dielectric material so that the effective separation between said mode suppressing conductors is less than one-half wavelength in said dielectric materialat the highest operating frequency of the circuit component, and

means for releasably securing said mode suppressing conductors in position between said outer conductors.

7. The circuit as claimed in claim 6 wherein each said outer conductor includes at least in part a relatively thin foil sheet of conductive 'material secured to said dielectric material and said dielectric material has slots therein extending generally parallel to said inner conductor, said mode suppressing conductors being disposed in the slots in said dielectric material.

8. The circuit according to claim 6 wherein said mode suppressing conductor has a plurality of electrical contact points spaced along its length, said contact points being spaced apart a distance less than a half wavelength at said highest operating frequency of the circuit.

9. The circuit according to claim 6 wherein said mode suppressing conductor includes a helix of wire.

10. The circuit according to claim 6 wherein said mode suppressing conductor includes a flexible member with a plurality of contact members disposed thereon and extending in opposite directions therefrom.

11. The circuit according to claim 6 wherein releasable securing means fastens said outer conductors together.

12. An electrical transmission line for propagating high frequency electromagnetic energy consisting substantially of a pure TEM mode,

a pair of planar outer conductors of indeterminate length positioned in superposed spaced relation,

a planar inner conductor of corresponding length positioned between said outer conductors and extending in a direction parallel to said outer conductor,

said inner conductor being narrower than said outer conductors,

solid dielectric material disposed between said inner conductor and each said outer conductor so that said inner conductor is supported in insulated, spaced relation with respect to said outer conductors by said solid dielectric material,

an elongated deformable mode suppressing electrical conductor, and

means for releasably securing said mode suppressing conductors between said outer conductors in electrical contact therewith and in parallel, spaced relation to said inner conductor.

13. The line according to claim 12 wherein said mode suppressing conductor includes a helix of metal wire.

14. The line according to claim 12 wherein said mode suppressing conductor includes a flexible member with a plurality of spring members disposed thereon, each said spring member having a pair of fingers and extending in opposite directions therefrom.

15. An electrical transmission line for propagating high frequency electromagnetic energy consisting substantially of a pure TEM mode,

a pair of planar outer conductors of indeterminate length positioned in superposed spaced relation,

a planar inner conductor of corresponding length positioned between said outer conductors and extending in a direction parallel to said outer conductor,

said inner conductor being narrower than said outer conductors,

solid dielectric material disposed between said inner conductor and each said outer conductor so that said inner conductor is supported in insulated, spaced relation with respect to said outer conductors by said solid dielectric material, itwo elongated, deformable, mode suppressing electrical conductors, said mode suppressing conductors being 63 positioned in electrical contact with both said outer conductors on opposite sides of said inner conductor, parallel to and spaced from said inner conductor by a said solid dielectric material so that the effective separation between said mode suppressing conductors is less than one-half wavelength in said dielectric material at the highest operating frequency of the circuit component, and

means for releasably securing said mode suppressing conductor between said outer conductors in electrical contact therewith and in spaced relation to said inner conductor.

16. An electrical transmission line for propagating high frequency electromagnetic energy consisting substantially of a pure TEM mode,

a pair of planar outer conductors of indeterminate length positioned in superposed spaced relation,

a planar inner conductor of corresponding length positioned between said outer conductors and extending in a direction parallel to said outer conductors,

said inner conductor being narrower than said outer conductors,

a sheet of solid dielectric material disposed on either side of said inner conductor and between said inner conductor and each said outer conductor so that said inner conductor is supported in insulated, spaced relation with respect to said outer conductors by said solid dielectric material,

a pair of slots in each dielectric. sheet, said slots being disposed parallel to each other and to said inner conductor,

two elongated, deformable, mode suppressing electrical conductors, said mode suppressing conductors being disposed in said slots in electrical contact with both said outer conductors on opposite sides of said inner conductor, parallel to and spaced from said inner conductor by said solid dielectric material so that the effective separation between said mode suppressing conductors is less than one-half wavelength in said dielectric material at the highest operating frequency of the circuit component, and

means for releasably securing said mode suppressing conductor between said outer conductors in electrical contact therewith and in spaced relation to said inner conductor.

References Cited by the Examiner UNITED STATES PATENTS 2,922,968 1/1960 Van Patten 333-84 2,937,347 5/1960 Mathaei et al. 333-84 2,984,802 5/1961 Dyer et al 333-84 3,135,935 6/1964 Englebrecht 33384 HERMAN KARL SAALBACH, Primary Examiner.

R. F. HUNT, Examiner. 

1. A MICROWAVE CIRCUIT COMPONENT COMPRISING A PAIR OF OUTER CONDUCTORS OF INDETERMINATE LENGTH POSITIONED IN SUPERPOSED SPACED RELATION, A CONDUCTOR OF CORRESPONDING LENGTH POSITIONED BETWEEN SAID OUTER CONDUCTORS AND EXTENDING IN A DIRECTION PARALLEL TO SAID OUTER CONDUCTORS, SAID INNER CONDUCTOR BEING NARROWER THAN SAID OUTER CONDUCTORS, DIELECTRIC MATERIAL DISPOSED BETWEEN SAID INNER CONDUCTOR AND EACH SAID OUTER CONDUCTOR SO THAT SAID INNER CONDUCTOR IS IN INSULATED, SPACED RELATION WITH RESPECT TO SAID OUTER CONDUCTORS, AN ELONGATED MODE SUPPRESSING ELECTRICAL CONDUCTOR, AND MEANS FOR RELEASABLY SECURING SAID MODE SUPPRESSING CONDUCTOR BETWEEN SAID OUTER CONDUCTORS IN ELECTRICAL CONTACT THEREWITH AND IN SPACED RELATION AND SUBSTANTIALLY PARALLEL TO SAID INNER CONDUCTOR. 